1. Field of the Invention
The present invention relates generally to an internal combustion engine and more specifically to an induction system heating arrangement which is load responsive.
2. Description of the Prior Art
One well known method of heating an incoming charge (air or air-fuel mixture) flowing through the induction manifold toward the combustion chamber or chambers of the engine, includes directing some of the engine exhaust gases into a heating chamber formed about a suitable portion of the manifold (usually the riser bottom) and controlling the temperature to which the manifold rises using a temperature responsive bimetallic strip to operate a flap or like arrangement which throttles the amount of exhaust gas circulated through the chamber. However, this arrangement has suffered from the drawback that the temperature of the exhaust gases, due to the heating of the incoming charge, tend to be insufficient during engine warm-up and/or low temperature operations, to promote adequate oxidation of noxious components (e.g. HC and CO) in purifying device such as catalytic converters etc.
Another well known method of heating the induction manifold takes the form of circulating some of the water from the coolant jacket through a jacket formed along the bottom of the induction manifold. This, while solving the above mentioned exhaust gas purification problem has encountered drawbacks in that efficient heating is not possible until the bulk of the coolant (water or the like) has been heated to a temperature whereat a useful amount of heat exchange is possible and in that additional energy is required by the coolant circulation pump to circulate the coolant through the additional chambering. Thus, during cold engine starts effective heating and carburetion of the air-fuel mixture fed to the combustion chambers is poor. Further, once the engine has warmed up, the heating continues irrespective of the mode of engine operation, degrading the charging efficiency of the engine during high speed and high load operation.
One attempt to overcome the above mentioned problems has been proposed in Japanese First Provisional Publication Sho 56-32071. In this arrangement each of the cylinder liners and structure defining the cylinder heads are covered in porous ceramic layers which act as wicks. Engine coolant is supplied to the coolant jacket wherein it is absorbed by the layers and subsequently converted to its gaseous form. The incoming charge is heated by some of the gaseous coolant which is permitted to pass through conduit 11 into a heating chamber 12 located beneath the induction manifold riser.
However, this arrangement has proven impractical in that it suffers from the notable drawbacks that adequate cooling of the engine is not possible and the ceramic layers readily undergo thermal damage and in that the incoming charge is heated during all modes of engine operation.